Watery red eyes, runny nose, sneezing, coughing—these familiar symptoms mean spring is in the air. Millions of people suffer from seasonal allergies triggered by airborne pollen—not just in spring but in summer and fall, too—and now evidence suggests their numbers will rise in a changing climate. The evidence so far is preliminary, but it points to a confluence of factors that favor longer growing seasons for the noxious weeds and other plants that trigger seasonal allergies and asthma attacks. Carbon dioxide (CO2), in addition to being the principal global warming gas, can also be thought of as plant food—it's the source of carbon needed to make sugars during photosynthesis. When exposed to warmer temperatures and higher levels of CO2, plants grow more vigorously and produce more pollen than they otherwise would.[1,2]
Physicians who treat allergic airway diseases are already reporting an uptick in symptoms that they attribute to climate change. In a statement published last year, the World Allergy Organization, comprising 97 medical societies from around the world, opined that climate change will affect the start, duration, and intensity of the pollen season and exacerbate the synergistic effects of pollutants and respiratory infections on asthma.
"We're seeing increases in both the number of people with allergies and what they're allergic to," says Leonard Bielory, a professor and allergy specialist at the Rutgers University Center of Environmental Prediction and attending physician at Robert Wood Johnson University Hospital. "Should warming continue," he says, "then more people will be exposed to seasonal allergens with subsequent effects on public health."
Pollen (gold spheres) is produced by the stamens (gray), which are the male reproductive organ of the flowering plant. Pollen grains are covered in proteins that assist in reproduction but also trigger allergic reactions in sensitized people. © Martin Oeggerli/Science Source
Environ Health Perspect. 2016;124(4):A70-75. © 2016 National Institute of Environmental Health Sciences